Cutting equipments of this type are generally used in complex systems for the automatic processing of documents comprising high speed printers and unwinding devices which operate on continuous forms of paper webs. These equipments provide to separate the continuous form into singular or discrete printed documents for the following processing.
For the production of standard documents the times necessary for the cutting of the forms, the separation of the sheets, the finish and the collection of the documents are well longer with respect to the times associated to the print.
In fact, the high speed printers can work in continuous. Instead, the cutting equipments and the finishing apparatuses must be periodically stopped for allowing the manual removal and collection of the documents.
A buffer store for the printed and not yet cut form can be provided between the high speed printer and the cutting equipment. Despite it and in dependence on the interruptions, the general productivity of the system results limited by the times of cutting.
Typically, a cutting equipment for continuous forms includes an input moving device and a cutting mechanism with a transversal blade. The moving device introduces the form at a velocity which, in average and in the case of on-line connection, must be equal to the delivery velocity of the printer.
The velocity of the forms can be sufficiently high in cutting equipments having helicoidal rotating blades with cutting on the fly and the use of these equipments in the systems of automatic processing of documents is not penalizing. Nevertheless these equipments result particularly expensive in the purchase and in the maintenance.
In the equipments in which the blade is operated in intermittent way the form must be stopped and, upstream of the cutting mechanism, a feeding device is provided for stopping the form before the cutting and accelerating it immediately after the cutting. A loop forming device, interposed between the moving device and the feeding device, allows the section of form to be cut to be moved according to a law of motion different from the law of motion of the entering form.
The velocity of cutting depends on the times required for the stop and the start of the section of form to be cut, for the stabilization of the loop and for the execution of the cut. These times are naturally conditioned by the variability of response of the involved mechanisms, by the transmission of the control of movement to the form and by the interaction of the mechanisms with the characteristics of the form. The velocity is also influenced by the times of contact of the form with the moving blade.
The involved parameters impose that, for an acceptable reliability of a cutting equipment, the stroke of the blade should be rather extended. Further, sufficient delay times should be provided between the stop of the feeding device and the start of the cutting mechanism and, respectively, between the end of the cutting and the start of the feeding device.
The cutting equipments which operate while the form is at rest are much less expensive than the cutting equipments operating on the fly but, still today, the obtainable cutting velocity represents a limit to the productivity of the automatic processing of documents using these equipments.
A cutting equipment with reciprocating blade, in which the paper web is introduced at constant velocity and providing a loop forming device is known. The cutting feeding device includes a clamping device for intermittent clamping the web, a conveyor with a continuously driven transport roller, a pressure roller with a high coefficient of friction and a lifting device controlling the pressure roller for accelerating and braking the section of form to be cut. For this equipment and form length of 30 cm (12″), a cutting performance of up to 36.000 cuts per hour is hypothesized.
Despite these expectations, the cutting equipments commercially available have a production of around 25.000 single sheets per hour and form of 12″. Such value is well less of what is desirable, particularly when the cuts are performed, out of the line of the printers, on pre-printed forms, wound in rolls or folded up in stacks. In particular, also the above known equipment has problems in transmitting the start and stop commands to the section of form to be cut.
Another problem of the cutting equipments operating while the form is at rest arises from the fact that the formation of the loops is a source of notable noise and instability with risks of tears in the web and errors in the cuts.
A cutting equipment in which the loop develops upwardly with respect to the movement surface of the web for the action of an air jet is also known. A control means controls both the input moving device and the cutting feeding device to stop the input moving device when the loop reaches a predetermined maximum height, starts thereafter the cutting feeding device and, in sequence, starts the input moving device.
Also in this device the length of the entering form and the length of the loop section are subjected to accelerations and brakes with tensions on the incoming form, risks of slippage and limitations on the obtainable cutting speed.